Process of converting substances ionized in solution, with the help of ion exchangers



Nov. 20, 1956 J- A. ZEEGERS 2,771,418 I PROCESS OF CONVERTING SUBSTANCES IONIZED IN SOLUTION, WITH THE HELP OF ION EXCHANGERS Filed Oct. 15, 1952 I 1 7 2 1 m-u m I I l B1A1 l W l F H20 I i v 1 2 H n-i n g B1A1 I J l 1 l l E1 E2 |E 1 Ep l I J l l J l United States Patent 1 O PROCESS OF CONVERTING SUBSTANCES ION- IZED IN SOLUTION, WITH THE HELP F ION EXCHANGERS Johannes A. Zeegers, Sittard, Netherlands, assignor to Stamicarbon N V., Heerlen, Netherlands Application October 15, 1952, Serial No. 314,832 Claims priority, application Netherlands October 24, 1951 Claims. (Cl. 210--24) The present invention relates to a process of converting substances which are ionized in solution (i. e., bases, acids, salts) with the help of ion exchangers and, more particularly, the invention pertains to a method of regenerating the ion exchanger used in this conversion process.

Field of invention It has previously been proposed to cause the conversion of two soluble salts B1A1 and BzAz, with the help of ion exchangers, to proceed in such a manner that two diiferent salts BIAZ and B2A1 are obtained according to the equ In order to realize this conversion, an ion exchanger, hereinafter denoted by the abbreviation I.E., is utilized which contains the ion B1 and is capable of exchangingthis ion B1 for the ion B2, when a salt solution in which the ion B2 is present is led over the LE.

The first phase of the process, the so called loading of the I.E., may be represented by the equation:

The I.E., which is now charged with B2 ions, is subsequently Washed with. water and thereafter regenerated by passing a solution of the salt- B1A1 over it.

The second phase of the conversion process, the socall'ed regeneration of the I.E., may be represented by the equation:

By addition of the equations (2) and (3) supra, it will be seen that a double conversion is obtained between the salts BIAI and BzAz, as a result of which the salts B1A2 and B2A1 are formed, the LE. having only func- B1 ions to be exchanged difiers in its behavior with respectto the B2 ions, this difference being due to the fact that the ion B2 is more firmly bound to the LE. than the ion B1, so that the regeneration of the IE. is more difiicult than the loading thereof.

By the term loading of the I.E., as used in this specification and the appended claims, is to be understood the process in which the LE, containing a particular ion is contacted with a solution containing another ion which it is desired to substitute for the ion of the LE. and which is more firmly bound by the LE. than the one which the IE. is to release. The term regeneration, as used in the specification and claims, stands for the process wherein the LE. loaded with a particular ion obtained from a solution with which the LE. has been treated, is conis, on an average, 1.

2,771,418 Patented Nov. 20, 1956 tacted with aregeneratingsolution containing another ion.

.is more firmly bound by a certain LE. than the ion B1, the result will be that the loading according to the equation [B1.I.E.] +B2- [B2.I.E.] +B1 in a limited number of columns arranged in series and filled with B1.I.E., can be carried out in such a manner that a pure B2A2 solution fed at one end of the series of columns. can always be discharged at the other end as a pure B1A2 solution.

With such a load, it appears that a stationary transition zone moves through the columns, so that on the feeding side of this zone, the solution present in the columns and the LE. contain exclusively B2 ions, and the solution and the LE. at the discharge side of this zone contain exclusively B1 ions, whereas in the transition zone itself, the proportion +,B in the solution and on the LE. gradually changes, during which process all the proportions between 1 and 0 are traversed.

However, the length of this transition zone is constant and the dimensions of the columns are always chosen so that the whole transition zone lies within one column or a few columns.

' In a regeneration process according to the equation:

it will be seen that such a stationary transition zone of constant length will not be formed. That is, if an IE. contained in a number of columns arranged in series and loaded with the firmly bound B2 ions is regenerated by adding to the first column a solution of the ion B1, which is less firmly bound by the LE. than the B2 ion, the transition zone formed in the column moves and also keeps increasing in length. Only by means of a constantly increasing number of columns can the solution present in the columns and the LE. itself on the feeding side of this transition zone be made to contain exclusively B1 ions and at the other side of this zone the solution and the'LE. to contain exclusively B2 ions, while over the length of the transition zone and in the direction of the liquid current the proportion changes from 0 to 1.

In technical practice, however, it is only possible to carry out the continuous regeneration process in a limited and constant number of columns arranged in series. It follows, therefore, that in the regeneration carried out in this manner, it is impossible to obtain both a complete regeneration and a liquid discharging from the last of the series of columns consisting exclusively of a solution of the cation Bz, which means that in all cases, a solution is obtained in which the proportion As a result, the regeneration has been carried out with an excess amount of regencrating solution containing the ion B1 with respect to the amount of [Bz.I.E.] regenerated. Such use of an excess of regenerating solution is not a drawback, provided the regenerating agent is an inexpensive salt, the

solution of which as such is obtainable in large amounts. For instance, the previously proposed preparation of NaNO;; by converting a Ca(NO3)2 solution with sea water with the help of an I.E. can be effected economically without recovering the regenerating agent NaCl. In this case, the solution obtained in the regeneration is nothing but sea water which has become poor in NaCl and has some CaCl2 dissolved therein. Such a solution contains no valuable components and may, therefore, be directly pumped into the sea without objection.

However, in the corresponding preparation of KNOa, by converting a Ca(NO3)2 solution and a KCl solution, the liquid discharging from the last column during the complete regeneration of the LE. loaded with Ca ions, contains, besides CaClz, a considerable amount of KCl and this liquid cannot, therefore, be considered worthless.

It has now been found possible to carry out the complete regeneration of the LE. in a limited number of columns in such a way that the liquid leaving the last column contains a virtually pure solution of only one salt. Thus, when making KNOs, by converting solutions of Ca(NO3)z and KCl, it is possible to obtain, according to the invention, a final liquid consisting of a virtually KClfree CaClz solution, by regenerating with a KCl solution an IE. loaded with Ca ions. Furthermore, little or none of the KCl used as regenerating agent is lost.

Objects The principal object of the present invention is the provision of a novel method for the regeneration of ionexchangers, or columns filled with such ion-exchangers, which method is free from the disadvantages noted above in connection with prior regeneration techniques.

Other objects include:

(a) The provision of an improved method for the regeneration of a series of columns containing the ionexchanger to be regenerated, whereby substantially completely regenerated ion-exchanger columns are obtained at one end of the series and a solution of spent substantially completely converted regenerating agent is obtained from the other end of the series.

(b) The provision of an improved method for the regeneration of a series of a limited but constant number of columns containing the ion-exchanger loaded with the ion to be replaced, whereby there may be obtained from the last column of the series a substantially pure aqueous solution, of a compound of the ion removed from the ionexchanger.

(c) The provision of an improved process for the double conversion of solutions of salts, acids or bases, using a series of columns containing an ion exchanger and involving novel improvements in regenerating the ion-exchanger, whereby both completely a regenerated column and a completely converted regenerating agent are obtained.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Description Briefly stated, the objects outlined above are realized, in accordance with the present invention, by carrying out the regeneration phase of the conversion procedure in three successive stages, rather than in a single stage as has previously been the case, with the series of columns containing the ion exchanger to be regenerated set up into two groups.

More specifically, the present invention provides the improvements in a process for regenerating an ion-ex- 4 changer by passing a solution of a regenerating agent successively through a series of columns containing the ion-exchanger loaded with the ion to be replaced and withdrawing regenerated ion-exchanger from the first of the series and a solution of spent substantially completely converted regenerating agent from the last of the series, comprising the steps of dividing the series of columns into two groups and passing an excess of regenerating agent through the first group, removing excess regenerating agent from the solution discharged from the first group of columns, thereafter, passing said solution through the second group of columns, collecting the substantially completely converted regenerating solution from the last column of the second group, cutting out the first column of the first group and making the first column of the second. group the last of the first group, introducing a new column filled with untreated ion-exchanger loaded with the ion to be replaced at the end of the second group and, thereafter, repeating said operation.

The regenerating method according to the invention is not only applicable to the preparation of KNO: by double conversion of KCl and Ca(NO3)2 solutions with the help of an ion-exchanger, but in principle, the process may be used advantageously for many double conversions between ionog'enic substances, in which a series of successive loadings and regenerations of the ion-exchanger, according to the above-mentioned Equations (2) and (3) are employed, namely:

These loadings and regenerations are interrupted only by washing with water of the amount of BzAz or B1A1.

solution still contained in the free space between and in the LE. grains.

In order that the invention may be more readily understood, the manner of carrying the invention into effect is hereinafter described with reference to the accompanying drawings, in which:

' Figure 1 is a flow diagram of the regeneration, and

Figure 2 is a flow diagram of the loading of the columns containing the ion-exchanger.

In Figure 1, C1, C2 Cm represent a first group of a limited number (m) of columns arranged in series; D1, D2 Dn represent a second group of a limited number (n) of columns arranged in series, and Ev and Cr represents, respectively, an evaporator and crystallizer arranged between the two groups of columns to be regenerated.

- In Figure 2, E1, E2 Ep represent a series of a limited'number (p) of columns to be loaded.

In carrying out the regeneration process, according to the invention,'a solution of BrAiis admitted to the first column C1 in the first stage and'permitted to flow through the following columns C. Thus, a virtually stationary state is created in this group of columns, so that the ion-exchanger in column C1 is fully regenerated after a certain time and, therefore, only contains B1.I.E. In the remaining columns C, the ion-exchanger is to some extent regenerated with B1 ions, but contains B2 ions as well, in such a manner that the proportion B2 B1+B2 on the ion-exchanger shows a continuous increase per column in the direction of the liquid current. Thus, the last column Cm contains an incompletely regenerated LE. and the liquid to be discharged therefrom consists of a solution containing both B1A1 and BzAz, in which the proportion The second stage of the regeneration consists in taking the liquid from the'column Cm and freeing the same, as

inafter described, of one or both of' B1A1 and B'zAz to such an extent that in the liquid the proportion state being attained in which the columns D will cometo contain an ion-exchanger loaded with both B1 and B2 ions in such a manner than the last column Dn contains an ion-exchangerwhich is almost entirely unregenerated [B2..I.E.]. From .this last column Dn, a B2A1 solution is discharged whichis virtually free from regenerating. agent BiAi, the preceding-columnscontainingv an. ion-exchanger with: am increasing. degree of regeneration". This means that: the proportion;

B1+-B2 onthe ion-exchanger constantly increases from Dr to Dn.

According'to the invention, the completely regenerated column C1, at the side where the'regenerating agent is supplied, is put out of the circuit at the end of a certain lapse of time, i. e., the regeneration period. However, the series of columns is recom'pleted by adding a new column containing ion exchanger which is completely unregenerated, the feed and discharge of the two groups ofcolumns at. the same time being subjected to an alteration such, that the first column of group D is moved over to group C and becomes Cm, Anew regeneration period isthen begun whereby one more column, the first of the first stage, is completely regenerated.

In the transition from one. regeneration period; to the following one, it will be appreciated that a column at one side of-ythe series of columns 'C is put out of the circuit, while at the other side a new column is added. In thisway, the total number, of columns subjected to a regeneration treatment perregeneration period is always the same. Thus, column Cz"will"co me to function as C1 in the preceding period, column Ca will come to function as C2 in the preceding period, column Cm will come tofunction as Cm r in the preceding period, column D1 will come to function as Cm inthe preceding period, column Dz will come to function as Dr in the preceding period, etc. Dn will come to' function as Dn1 in' the preceding period, and the new column added willcome to functionas'D in the preceding period.

'At the end of the subsequent regeneration period, column C2 is put'out of the circuit and the other columns" are again rearranged with the addition ofjstill another new column in the manner denoted above.

The success of the invention is due, at least to a large extent,, to the splitting up of the regeneration into three stages and the corresponding change effected in the composition of the solution traversing the groups of columns 6 and D'during one regeneration period by virtue of the removal, as by crystallization, of excess regenerating agentin the second stage 'ofthe regeneration. These features make it possible. to use a limited and constant number of columns to regenerate the ion-exchanger completely without the drawbacks involved if anlever widening transition zone moving within the columns is allowed to build up and with the advantage that a simple solution of B2A1 virtually free from the regenerating agent BiAr originally supplied to the columns can be obtained as discharge fromthe last column.

As to the extent the composition of' the liquid is to be changed by the crystallization, this is determined by the excess or regenerating agent Bi-Ai supplied to the group of columns C. per regenerationperiod. As already stated, every time a new regeneration period is started, a new column of [B2.I.EL] is added and a column with an equivalent amount of [B1.I.E.l is put out of the circuit. When the number of ions attached to the IE. is Q equivalents per column, and to the first column of group C an amount of regenerating agent BiAi equal to kQ equivalents is fed per regeneration period, not'taking into consideration the amount of solution needed for filling the free space between the grains of ion-exchanger, it is neces-- sary to remove from the liquid discharging from the column Cm, (k-1)Q equivalents of BiArby crystallization.

It occasionally happens that from the last column no solution is discharged which is substantially free from B1A1, although the excess of B1A1 used for regeneration in the second stage of the regeneration process has been removed. In order to avoid this, it is also advisable to remove a relatively small amount of B2 ions from the regenerating liquid inthe second stage of the regeneration process. Often, however, it is not possible to remove an; amount of B2A1 by crystallization, especially if the B2A1 substance is very soluble. In such cases, the desired effect can be reached by allowing an insoluble B2 compound to form in the solution by adding, for instance, the compound BlA3 to a solution containing both BiAr and BzAr. By doing this, B2Aa precipitates and an equivalent amount of BIAI is dissolved. This newly-formed amount of BiAi should then be removed by crystallization together with the excess of B1A1. The amount of B2 ions to be removed cannot be determined exactly and must be ascertained experimentally in those cases where it isiound that, after removing B1A1 in the secondstage of the regeneration process, thesolution discharged from the last column is not practically free from BlAl. In practice, however, it. has been foundthat it generally suffices to remove only a relatively small quantity of B2 ions.

The loading of the regenerated columns may be carried out in the conventional way shown in Figure 2, i. e., by

admitting a solution of BzAz tothe first column of a group consisting of a limited number (p) of columns (E) filled with [B1.I.E.] and arranged in series, after which the solution is permitted to flow through the succeeding columns; In this way, a virtually stationary state is created ini-this series of columns (B) so that the LE. in column E1 is fully converted after" a certain time, and therefore only contains [B2.I.E.l. The succeeding columns contain an LE. which is to some extent loaded with E2 ions, but carries B1 ions as well, such that the proportion B1 B1+B2 on. the LE. shows a continuous increase per column in the direction of the liquid current. Hence, the last column Ep contains a very incompletely loaded I.E., while the liquid to be discharged from this column consists of a solution-of B1A2.

The completely loaded column E1, at the side where the loading agent is supplied',;is put out of the circuit at the end of a certain lapse of time, i. e., at the end of the loading. period. The series of columns'is recompleted' by adding anew column containing ion-exchanger which is fully regenerated, i. e., one to be loaded, and a new loading period begun, in which just the first column is completely loaded.

The total number of columns subjected to a loading treatment per loadingperiod is always the same. Thus in thenew' loading period: column Ez will come to function as E1 in the preceding period, column Ep-l will come to function as E -z in the preceding period, column En will come to function as E -r in thepreceding period, and the" new fully regenerated column added will come to function asE in the preceding period.

The following examples illustrate further the nature of the invention and the manner in which it may be carried into effect.

EXAMPLE I In the preparation of KNOs from solutions of KCl and Ca(NOs)2 with the help of an IE. consisting of sulfonated styrene (the normal trade product Dowex-SO) use was made of columns each of which contained 100 litres of LE. The capacity Q per column amounted to 218 equivalents CaO. The free space between the LE. grains in the column had a volume of 40 litres.

The regeneration of the columns loaded with Ca ions was carried out in such a manner that for each regeneration period six columns were traversed by the regenerating liquid, the columns being arranged in two groups of three columns each. During one regeneration period, a 37% KCl solution was fed to the first column of the first group at 90 C. A total of 198 kg. of solution was fed to the first column. This means 3.3 Q equivalents of KCl+52 kg. 37% solution, which is the 40 litres remaining behind in the free space between the LE. grains that are removed from the cycle when the column is taken out of the system. From the third column of the first group a total amount of 196 kg. of solution was discharged, first 52 kg. present in the free space and after that 144 kg., the mean composition of which was as follows:

The 196 kg. of solution were concentrated, during which process 67 kg. of water were evaporated, and the liquor subsequently cooled, so that 2.3 equivalents=37 kg. of KCl were crystallized out. After centrifuging, the mother lye (92 kg.) of the following composition 5.5% KCl 29% CaClz (y2=0.88) 65.5% B20 was fed to the first column of the second group.

During the regeneration period first 30 litres of water were discharged from the last column of this second group (water present in the free space between the grains of I.E., which was displaced by the in-flowing regeneration liquid), after which 49 kg. of a solution having the composition 0.8% KCl 26% CaClz 73% H2O were removed. The first column of the first group was fully regenerated and put out of the circuit, after which a new column was added to the second group and another regeneration period with six columns arranged in two groups of three columns each, was started up.

EXAMPLE II Forthe preparation of NaNOs by double conversion of NaCl and Ca(NO3)z use was made of the same I.E. in the same columns as described in Example I.

In the regeneration process of the LE. loaded with Ca ions, six columns in series, arranged in two groups of three columns each, were again employed.

' To the first column of the first group, a 26% NaCl solution at about 20 C. was fed in, so that for each regeneration period a total of 146.3 kg. of solution was supplied. This corresponds with 2 Q equivalents of NaCl+40 litres of solution for the free space.

During this period, the first 40 litres ofsolution (about 48 kg.), contained inthe free space, were discharged from 8 v the third column of the first group, and then solution with a mean composition of:

8.7% CaClz 17.0% NaCl 74.3% H2O To this solution, 4.75 kg. of NazCOs (89.6 gram equivalents) were added after which the resulting CaCOa precip itate (4.48 kg.) was removed by filtration. Thereafter, 53.6 kg. of water were removed by evaporation after which by cooling and centrifuging 18 kg. of NaCl were removed from the resulting mother lye.

The rest of the mother lye, 26.5 kg. in all and having a composition of 13.3% CaClz 14.5% NaCl 72.2% H2O was supplied to the first column of the second group, together with the 40 litres which had previously been discharged from the last column of the first group of columns. From the last column of this group first 30 litres of water were removed per regeneration period and, subsequently, 36 kg. of solution which contained only a trace of NaCl along with 19.8% of CaClz and 80.2% of H20.

A new regeneration period was started in which the column that had been totally regenerated in the preceding period was first put out of the circuit and a new column to be regenerated thereafter added.

EXAMPLE III Magnesium chloride and potassium sulfate were prepared by double conversion of MgSO4 and KCl with the help of the anion-exchanger consisting of a polystyrene with quaternary N-groups (the normal trade product Dowex-2). While using a rather concentrated solution 1 molar), it was found that the CI-ion is bound more strongly by the LE. than the SO4-ion, so that the regeneration may be represented by.the equation:

MgSO4 solution retained in the free space between the.

LE. grains- From the third column of the first group the first 40 litres (about 52 kg. of solution) present in the free space were discharged and then 119.4 kg. of solution in all, of which the mean compositon was:

20.7% MgSO4 3.6% MgCl 75.6% H O eq. Cl

The solution was evaporated to such a degree that at 25 C. 48.8 kg. of MgSO4 were crystallized out and separated from the remaining mother lye (17.2 kg.) by centrifuging. The mother lye, having the composition 25% MgCl2 5% MgSO4 70% H2O was supplied to the first column of the second group of columns together with 40 litres of liquid discharged from the free space in the last column of the first group.

Per regeneration period 30 litres of water were discharged from thelast column of the second group after 97.8 kg'. of:

9 which there were obtained 27 kg. of a solution whose composition was:

17.5% MgClz 1% MgSOs 81.5% H2O After this a new regeneration period was started.

Summary As will be appreciated from the foregoing, the present invention provides a new and highly advantageous process for the regeneration of columns filled with ion-exchangers, particularly those used in carrying out double conversion between two salt solutions, e. g., the double conversion between KCl and Ca(NOs)2 to give KNOs and CaClz.

The regeneration process of the present invention possesses the advantage of enabling complete ion-exchange regeneration using a limited and constant number of columns containing the ion-exchanger to be regenerated, while avoiding the disadvantages involved if an everwidening transition zone moving within the columns is allowed to build up. At the same time, the present process possesses the additional advantage of permitting discharge from the regenerating columns of a single solution containing a compound of the ion removed from the ion-exchanger which is substantially free of the regenerating agent.

Furthermore, due to the new improved regenerating method described herein, it is possible to carry out a number of double conversions in a much more economical way than hitherto possible.

Having described my invention, what I claim is:

1. In a process for regenerating an ion-exchanger by passing a solution of a regenerating agent successively through a series of columns containing the ion-exchanger loaded with the ion to be replaced, wherein the series of columns is divided into a first group and a second group, and periodically the first column of said first group containing a regenerated ion-exchanger is removed from the series, the first column of said second group is made the last column of said first group, and a new column containing untreated ion-exchanger loaded with the ion to be replaced is connected at the end of said series, the improvement which comprises passing an excess of said regenerating agent through said first group, removing an amount of said regenerating agent substantially equal to that originally present as excess from the efiluent discharged from said first group, and thereafter passing said efiluent free from excess regenerating agent through said second group whereby a solution of spent, substantially completely converted regenerating agent is withdrawn from the last column of said series.

2. The method of claim 1, wherein excess regenerating agent is removed from the solution discharged from the first group of columns by evaporation to crystallize out the excess agent and the mother liquor freed from the resulting crystals of excess regenerating agent is fed into the second group of columns.

3. The method of claim 1, wherein a relatively small amount of the ion removed from the ion-exchanger is also removed from the solution discharged from the first stage along with the regenerating agent.

4. The method of claim 3, wherein the amount of the ion removed from the solution with the regenerating agent is precipitated by adding an equivalent amount of a compound comprising the active ion of the regenerating agent and forming an insoluble compound with the ion to be removed and, thereafter, filtering the liquid.

5. The method of claim 1 wherein the ion exchanger is loaded with Ca ions and the regenerating agent is KCl.

References Cited in the file of this patent UNITED STATES PATENTS 1,978,447 Austerweil et al. Oct. 30, 1934 2,252,065 Culligan Aug. 12, 1941 2,397,575 Tiger Apr. 2, 1946 2,458,115 Swensen Jan. 4, 1949 2,564,820 Smit Aug. 21, 1951 2,599,558 Juda June 10, 1952 2,689,229 Kimberlin Sept. 14, 1954 

1. IN A PROCESS FOR REGENERATING AN ION-EXCHANGER BY PASSING A SOLUTION OF A REGENERATING AGENT SUCCESSIVELY THROUGH A SERIES OF COLUMNS CONTAINING THE ION-EXCHANGER LOADED WITH THE ION TO BE REPLACED, WHEREIN THE SERIES OF COLUMNS IS DIVIDED INTO A FIRST GROUP AND A SECOND GROUP, AND PERIODICALLY THE FIRST COLUMN OF SAID FIRST GROUP CONTAINING A REGENERATED ION-EXCHANGER IS REMOVED FROM THE SERIES, THE FIRST COLUMN OF SAID SECOND GROUP IS MADE THE LEAST COLUMN OF SAID FIRST GROUP, AND A NEW COLUMN CONTAINIG UNTREATED ION-EXCHANGER LOADED WITH THE ION TO BE REPLACED IS CONNECTED AT THE END OF SAID SERIES, THE IMPROVEMENT WHICH COMPRISES PASSING AN EXCESS OF SAID REGENERATING AGENT THROUGH SAID FIRST GROUP, REMOVING AN AMOUNT OF SAID REGENERATING AGENT SUBSTANTIALLY EQUAL TO THAT ORIGINALLY PRESENT AS EXCESS FROM THE EFFLUENT DISCHARGED FROM SAID FROM GROUP, AND THEREAFTER PASSING SAID EFFLUENT FREE FROM EXCESS REGENERATING AGENT THROUGH SAID SECOND GROUP WHEREBY A SOLUTION OF SPENT, SUBSTANTIALLY COMPLETELY CONVERTED REGENERATING AGENT IS WITHDRAWN FROM THE LAST COLUMN OF SAID SERIES. 